I AM HELPING in a survey that may result in the reinstallation of some of the sewage lines outside a home and it's not easy. I already lost a weekend to this priority.
Some of the suspect 4" pipes expect water to flow uphill. You can actually see discrepancies in the starting and ending elevations of the lines without using any special laser equipment.
During the past month, several plumbers have measured the difference in elevation between start and ending points wherever the suspect sewage lines turn corners. One of the plumbers thinks the current pipe does not drop 1/4" per foot. In fact, one six metre section of pipe falls backwards.
I'm helping to dig up and reinstall the pipes but it's actually a job for a qualified engineer, so we're looking at Tradesmen.ie for ideas. I think the job requires a crew with construction laser measurement that corrects the current errors in the way the pipes lay in the ground. Too steep a drop and water flows over solid sewage instead of pushing it out into the main line.
I remember walking around the unfinished estate where these lines sit. Some of the open trenches did not include gravel or a solid surface laid under the pipes. That's a set-up for subsidence. In the current job, we probably need to pull up pipes, calculate the slope of the new line, install compacted gravel bedding beneath the pipe, and test the result.
Guys who have laid these kinds of pipes have recommended starting on the low end of the run and working up to the connecting point. I think the original crew laid the pipe in reverse because there's a problem with the way the last section sits above the ground surface. I also think the original crew did not backfill the waste pipe trench as they did the job. This probably helped the pipe to shift in its trench before the home's sewage system was commissioned.
Bernie Goldbach has a lot of DIY ahead.